In the past, rail vehicle positioning has been accomplished in two predominant manners. The traditional vehicle positioning system has used embedded track circuits which are insulated or electrically isolated sections of track with a voltage applied at one end, which are shunted by a vehicle and indicate that a vehicle is located at a certain segment of the track. Such a system is described in U.S. Pat. No. 4,361,301 entitled, "Vehicle Train Tracking apparatus and Method" and was issued to Donald G. Rush on Nov. 30, 1982, which is incorporated herein by this reference. Another improved system, has included dead reckoning with wheel tachometer readings which are corrected by trackside transponder units. Such a system is described in U.S. Pat. No. 4,027,840 entitled, "Vehicle Position Indicator with Radar Interrogation Each of Spaced Transponders Disposed Along Pathway for the Vehicle", which was issued to Peter Kenneth Blair on June 7, 1977, which is incorporated herein by this reference.
While these systems, or variations of them, have enjoyed use in the past, they each have several serious drawbacks. The traditional embedded track circuit method as a weakness, because it provides low resolution of position typically one or more miles. Also, there is no way to distinguish whether one or more trains are occupying the same track segment. The trackside transponder (or indicator) and wheel tachometer dead reckoning method has problems, because the wheel slip, between the locomotive wheel and the rail, causes uncertainty in the accuracy of the wheel tachometer. The ability to provide accurate position is also a function of the number of the expensive trackside transponders that are used.
The inability to continuously ascertain the precise location of a train on a rail network results in an inefficient use of the track resources because the dispatching, routing, or authorization of trains on a particular track is often delayed until all uncertainties of train locations about the network are resolved.
Consequently, there exists a need for improvement in rail vehicle positioning systems which have a high degree of accuracy while concomitantly reducing the need for trackside transponders.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a highly accurate rail vehicle positioning system.
It is a feature of the present invention to use a combination of sources including GPS technology, trackside transponders, track circuits and wheel tachometer readings to perform position determination.
It is an advantage of the present invention to provide position information over a wide geographic area without requiring trackside transponders over the entire length of track.
The present invention provides a rail vehicle positioning system which is designed to fulfill the aforementioned needs, satisfy the earlier propounded objects, contain the above described features and produce the previously stated advantages. The invention is carried out in a "trackside transponder-less" fashion, in the sense that the large numbers of trackside transponders which would be necessary if they were the sole source of position determination are substantially reduced along a large majority of the track length. Instead, the rail vehicle positioning system, utilizes a multiplicity of sources including track circuits, transponders, and GPS data to update the wheel tachometer and further uses GPS data to affect wheel tachometer calibrations.
Accordingly, the present invention relates to a rail vehicle positioning system which includes a GPS receiver, a reduced number of trackside transponders (or no trackside transponders), track circuits, a wheel tachometer and a computer which calibrates the wheel tachometer where available using GPS data and further performs a dead reckoning function.